Process for the oxidation of leuco bases for dyes



D. T. EWING ET AL Filed 001:. '7, 1927 PROCESS FOR THE OXIDATION OF LEUCO BASES FOR-DYES April 28, 1931.

, JM if @146 Patented Apr. 1931 UNITED STATES.

PATENT OFFICE nwrenr r. Ewmo m rnanx H. trons, or unsure, MICHIGAN P FOR THE OXIDATION OF LEUCO BASES FOB DYIS Applicationfled October 7, 1927. Serial Io. 224,728.

invention relates to processes for the oxidation of leuco-bases for dyes by means of an electric current, and includes special pparatus for carrying out the process heremafter describe The difierent leuco-bases of dyes are recogmzed chemical comgounds produced by recog mzed processes, an such producing processes form no part of this invention. The (process comprisin this invention is believe to ,be a new an useful method of oxidizing the leucoebase into the correspondmi fiarbmol base by electro-chemical action.

e drawing forming a part of this application is a vertical sectional view of the preferred form of the electrolytic cell for cal i iging out this process invention.

oughout the drawing and description the same number is used to refer to the same part. I

In carrying out this invention, the leucobase is dissolved in sulphuric acid with or without the addition of acetic acid. Acetic acid is necessary to give a product which will produce a crystalline dye. The sulphuric solution is then diluted to form a sufliciently dilute fluid of the desired volume. This solution is then passed through an oxidizing cell to which is applied a current of electricity having the necessary voltage and quantit to oxidize the leuco-base into the corresponding carbinol base. The carbinol base is then precipitated, washed and filtered. The steps of precipitating, washing and filtering the carinol base constitute no portion of t is invention as they are well known operations.

As an example of the operations followed in carrying out this invention, fifty grams of leuco-base were dissolved in 110 grams of'sulphuric acid. The solution was diluted to make 1200 cc. and placed in the anode compartment of the cell. A current of 15 amperes for two hours was passed through the cell. The temperature was 55 degrees C. A carbon electrode was used. No catalytic agent was employed. After the run the prodduct was neutralized with NaOH and a good roduct obtained. The catalytic agent has n dis nsed with; no stirring was neces- 60 sary, an the solution is maintained at substantially degrees C. by the heat given off due to the resistance of the cell. It was found that the addition of acetic acid will produce a very high grade product.

The apparatus essential for the carrying 55 out of this process invention comprises as illustrated in the drawings, a cell 1 made of wood suitably prepared, brick, cement or other material that will-withstand the action of the chemicals.

The cell has an inlet 2 and outlet 3 one of which is located'at the top and the other at the bottom of the cell.

' Two diaphra s 4 and 5 partition the cell as shown, and orm the end compartments 6 es and 7 within which are suitably supported the cathodes 8 and 9.

The anodes are horizontal lead plates 10 and 11, and it will be noted that one end of each plate is carried by a diaphragm. This invention is not limited to that construction. The

lates 10 and 11 are so arranged that the fluid om inlet 2 must pass against and around each overlying 1 plate until the outlet 3 is reached. The path thus interposed in the cell as the course which the fluid must take, is made very long, and it is such elongation of the path that is thought to be of advantage in this invention, operating as it does to bring about the complete oxidation of the leucobase continuously being passed through the cell. In the drawings it is shown that the lead plates are joined by a common vertical connector bar 12, which by a conductor 13may 35 be connected to the switch 14 which may be arranged to interrupt the current or to introduce for or less resistance-therein. From the switch 14 the connection is made with the no battery 15, or other source of current, and by way of the branching conductor 16 the con nection is made with the cathodes 8 and 9.

In the operation of this invention, it is believed that an inspection of the drawings will show that the fluid in passing through the cell must follow a very unusually long path. It is thought obvious that the speed with which the fluid moves or is moved may be controlled as desired by a variety of devices of well 1M known character and not necessary to be illustrated in this application.

Ha. now described this invention and explaine the manner of its operation, we claim A'continuous electrolytic rocess for the oxidation of leuco-bases capa hle of forming when oxidized coloring matter soluble in the fluid employed, consisting in dissolving the 10 leuco-base in a solution of sulphuric acid,

moving the solution back and forth in a horizontal direction through a much elongated path, subjecting the entire solution to the action of an electric current, and removing and 15 replacing at desired intervals portions of the materials acted upon.

In testimony whereof we aifix our signa tures. DWIGHT T. EWING.

FRANK H. LYONS. 

